tcpsrv.c

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <string.h>

// #define SRVPORT "49154"

struct msg_echo {
    unsigned short seq;
    unsigned short reserve;
    char msg[32];
};

int main(int argc, char *argv[])
{
    int sd, sd1, err, cnt;
    struct addrinfo hints, *res;
    struct sockaddr_storage sin;
    struct msg_echo echo;
    pid_t pid;

    socklen_t sktlen, len;
    char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];

    if (argc != 2) {
        fprintf(stderr, "Usage: ./tcpsrv <port number>\n");
        exit(1);
    }
    memset(&hints, 0, sizeof hints);
    hints.ai_flags = AI_PASSIVE;
    hints.ai_socktype = SOCK_STREAM;
    if ((err = getaddrinfo(NULL, argv[1], &hints, &res)) < 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(err));
        exit(1);
    }
    if ((sd = socket(res->ai_family, res->ai_socktype,
                     res->ai_protocol)) < 0) {
        perror("socket");
        exit(1);
    }
    if (bind(sd, res->ai_addr, res->ai_addrlen) < 0) {
        perror("bind");
        exit(1);
    }
    freeaddrinfo(res);
    if (listen(sd, 5) < 0) {
        perror("lisen");
        exit(1);
    }

    for (;;) {
        sktlen = sizeof(struct sockaddr_storage);
        if ((sd1 = accept(sd, (struct sockaddr *)&sin, &sktlen)) < 0) {
            perror("accept");
            exit(1);
        }
        
        pid = fork();
        if (pid < 0) {
            perror("fork");
            exit(1);
        } else if (pid != 0) {
            continue;
        }

        if ((err = getnameinfo((struct sockaddr *)&sin, len, hbuf,
                               sizeof(hbuf), sbuf, sizeof(sbuf), 0)) < 0) {
            fprintf(stderr, "getnameinfo: %s\n", gai_strerror(err));
            exit(1);
        }

        for (;;) {
            if ((cnt = recv(sd1, &echo, sizeof echo, 0)) < 0) {
                perror("recv");
                exit(1);
            }
            echo.msg[cnt - sizeof(unsigned short) * 2] = '\0';
            printf("%d bytes recved: IP %s, port %s, seq %d, msg %s\n",
                   cnt, hbuf, sbuf, echo.seq, echo.msg);

            echo.seq++;

            if ((cnt = send(sd1, &echo, sizeof echo, 0)) < 0) {
                perror("send");
                exit(1);
            }
            printf("%d bytes sent\n", cnt);
        }
        close(sd1);
    }
    close(sd);
}